The genes for Histidine UTilization (hut) in Klebsiella aerogenes are typical of a large number of genes whose expression is strictly regulated by the available supply of nitrogen. Thus nitrogen regulation of hut serves as a model system for this kind of pleiotropic control. The goal of the research proposed here is to develop an in vitro transcription system for the hut operon of K. aerogenes that is responsive to regulation by the nitrogen regulatory factor(s) and to study the molecular basis for that regulation. The specific objectives of the five-year proposal period are: (1) To determine the mechanism of carbon regulation at the promoter of the hutUH operon, (2) To begin an analysis of the nitrogen regulation at the promoter of the hutUH operon, and (3) To extend our understanding of the hut operons themselves.